Monday, October 25, 2010

Ubuntu 10.10 VNC Login Screen

I figured out how to get a graphical login screen over VNC on Ubuntu 10.10 today. The method that worked before Ubuntu 10.04 stopped working when XDMCP support was removed from gdm (source).

This procedure starts from a fresh install of Ubuntu-Desktop-10.10.

install xdm, vnc4server, and xinetd.
sudo apt-get install xdm vnc4server xinetd
When asked during installation what the default display manager should be, keep the setting as gdm.

Configure xdm to be able to answer XDMCP requests, comment out the following line in /etc/X11/xdm/xdm-config:
! SECURITY: do not listen for XDMCP or Chooser requests
! Comment out this line if you want to manage X terminals with xdm
!DisplayManager.requestPort:    0
Configure XDM to answer XDMCP requests from localhost, and to listen to just localhost by adding the following lines to /etc/X11/xdm/Xaccess:
LISTEN localhost

Configure XDM to not bring up a physical display by commenting out the following line in /etc/X11/xdm/Xservers:
#:0 local /usr/bin/X :0 vt7 -nolisten tcp

Configure the startup script to allow XDM to start despite gdm taking care of the screen by removing /etc/X11/default-display-manager:
sudo mv /etc/X11/default-display-manager /etc/X11/default-display-manager.disable

Add the VNC port definition to /etc/services if it has not already been added:
vnc 5900/tcp

Configure the VNC incoming port by creating /etc/xinetd.d/vnc:
service vnc
        only_from = localhost
        disable = no
        id = vnc
        socket_type = stream
        protocol = tcp
        wait = no
        user = nobody
        server = /usr/bin/Xvnc4
        server_args = -inetd -query localhost -once -SecurityTypes=None -pn -fp /usr/share/fonts/X11/misc/,/usr/share/fonts/X11/75dpi/,/usr/share/fonts/X11/100dpi/ -desktop Ubuntu
        log_on_failure += USERID
In this configuration connections are restricted to the local network (192.168.0.*).

After all these pieces are done, restart the services to load the new configurations:
sudo /etc/init.d/xdm restart
sudo /etc/init.d/xinetd restart

Now you should be able to use VNC to get a login screen.

There is a problem with gnome in this setup where it has a keyboard shortcut assigned to 'd', which can be fixed by going into System -> Preferences -> Keyboard Shortcuts and disabling, or reassigning the "Hide all normal windows and set focus to the desktop" shortcut key (source). This may happen because the default key binding is Mod4+D, and there is no Mod4 modifier key on the VNC connection.

Thursday, October 14, 2010

removing duplicate files

The challenge: Remove from one directory any file that exists in another directory, however the name of the files can not be used.

my solution:

first, make a list of the hashes of the files in each directory
find . -type f -print0 | xargs -0 shasum -a 256 > ~/tmp/files.lst
edit the file lists if necessary.

take a set intersection of the hashes
cut -f 1 -d ' ' list.txt | sort > hash.txt
comm -12 hash1.txt hash2.txt > clean.txt
the result is a list of just hashes in common between the lists.

list all the files with the selected hashes, using a perl script
#!/usr/bin/perl -w
use strict;

if(@ARGV != 2) {
    die "use: select hashes list\n";

my %hashes;
local *IN;
open(IN, "<", $ARGV[0]) or die "open: $!";
while(<IN>) {
    $hashes{$_} = 1;

open(IN, "<", $ARGV[1]) or die "open: $!";
while(<IN>) {
    my ($hash) = m,^(\S+), or next;
    $hashes{$hash} or next;
    print $_;

invoked like
perl clean.txt list1.txt | cut -c 67- > remove.txt
which results in a list of file names in the first list for files that also exist in the second list.

finally, remove the files
while read x ; do rm -- "$x"; done < ~/tmp/remove.txt